Conventionally, alkalinity is monitored by titrating an aqueous sample in the laboratory with a standardized sulfuric acid solution, as described in Standard Methods, APHA, 14th Ed., pages 278-282 (1976), and free carbon dioxide is monitored by titrating an aqueous sample with a standardized alkali solution such as sodium carbonate or sodium hydroxide, as described in Standard Methods, pages 298-300. Chemicals are then added to the aqueous solution from which the sample is taken, for various purposes such as to adjust alkalinity, cause coagulation of undesired contaminants or to reduce the hardness of the water.
In a biological system such as a water and waste water treatment system, the most meaningful alkalinity value is a measurement of the total alkalinity attributable to carbon dioxide, bicarbonate ion and carbonate ion. One difficulty with the conventional alkalinity titration method is that the alkalinity value determined represents the bicarbonates, carbonates and hydroxides present in the sample.
It is known to sample ground water, sea water, carbonated beverages and wine, and to measure the pCO.sub.2 of the sample using a pCO.sub.2 probe. This type of prior art is illustrated by the "Instruction Manual" for carbon dioxide electrode model 95-02 published by Orion Research. In this Manual, the user is instructed to adjust the pH of the sample to 4.8 to 5.2 prior to using the pCO.sub.2 probe. A substantial problem with such a procedure is that total pCO.sub.2 is not measurable at the required pH since a minor amount of carbon dioxide is still present as bicarbonate ion. In addition to this problem, this type of prior art has other deficiencies. It fails to minimize the loss of carbon dioxide to the atmosphere since the procedure is carried out in a system that is open to the atmosphere. Thus, loss of CO.sub.2 occurs in handling the sample and in analysis. Also, this type of prior art fails to actively adjust the sample temperature to a selected temperature and then maintain the sample at the selected temperature. Rather, this art only provides for passive temperature equilibration of the sample. Furthermore, this type of prior art does not provide for automatic pH adjustment of the sample but rather provides for a manual adjustment. Moreover, this type of prior art merely measures pCO.sub.2 and does not use the result obtained from the measurement to control the total alkalinity.
Other art using carbon dioxide sensors is exemplified by U.S. Pat. Nos. 3,147,081, 3,398,079, 3,673,069, 3,705,088, 3,709,812, 3,719,576 and 3,957,613. This art also uses these sensors only for monitoring purposes, with the primary use being in analyzing small liquid samples such as blood. The probe of U.S. Pat. No. 3,957,613 is capable of simultaneously sensing ion concentrations and partial pressures of gases in a sample, and has been suggested for use in environmental control, sewage being an example.
The use of a pH probe or of a probe capable of sensing dissolved oxygen, ammonia or sulfur dioxide, for only monitoring purposes, has been considered in cooling tower water systems. See Betz Handbook of Industrial Water Conditioning, 7th Ed., page. 241 (1976).
Finally, it is known to use a pH sensor in an apparatus for increasing the pH of waste water. This type of sensor is deficient in that it cannot measure the total alkalinity attributable to carbon dioxide, bicarbonate ion and carbonate ion. Exemplary of this type of prior art is U.S. Pat. No. 4,116,834 to King.
This and the other prior art of which I am aware is deficient as failing to provide a method for continuously monitoring and controlling the total alkalinity attributable to carbon dioxide, bicarbonate ion and carbonate ion, in an aqueous solution in which it is desirable to maintain alkalinity within a closely controlled range for environmental purposes, and is deficient as failing to provide a method for continuously monitoring the total alkalinity attributable to carbon dioxide, bicarbonate ion and carbonate ion of a natural body of water for environmental purposes.